[ludwigvolcano]

Can anyone tell me why an alloy of lead and tin is weaker than one of tin and zinc and also has a lower melting point?   

Is it due to lead having a higher electron affinity than zinc, or is it due to the different lattice structure (such as lead having a face centred cubic structure and zinc having a hexagonal close packing sructure), or to the different physical properties of the metals (such as zinc having a higher melting point than lead), or perhaps due to the way grains and dislocations form in the alloy?  I think both alloys have a substitutionary structure rather than an interstitial structure based on the metallic radii of the 3 elements. Or is there some other reason or combinations of the above?   

Many thanks in advance

Bob